1. Field of the Invention
The present invention relates generally to traffic control systems, and in particular to a method and apparatus for providing a driver with information concerning an imminent traffic signal change and the driver's distance from the intersection.
2. Description of the Prior Art
Traffic control systems have heretofore been associated with a wide variety of vehicle traffic conditions. The objectives of such systems generally include safety and transportation efficiency. In efforts to achieve such objectives, intersections which are traversed by vehicles have heretofore been provided with various traffic control systems. Stop signs and yield signs are often employed at relatively low-volume intersections. Intersections with greater volumes of traffic are often provided with traffic signals, which may comprise traffic light assemblies including individual signal light units having different colors and configurations for controlling traffic.
In the United States, such traffic control devices are governed by the Manual on Uniform Traffic Control Devices (MUTCD). In most jurisdictions compliance with the various traffic control systems is required by law. Furthermore, the requirements placed on motorists by certain traffic control systems are almost universal. For example, a continuous red light at an intersection normally prohibits entry into the intersection until the red light is replaced by a green light, at which time the motorist can proceed through the intersection. Normally, a yellow light is displayed after the green light interval and before the red light interval for the purpose of warning motorists that only a limited time remains to traverse the intersection before cross traffic will be permitted to enter the intersection pursuant to a green signal.
The yellow light interval is normally long enough to permit a motorist to either: (1) clear the intersection before the red light interval; or (2) stop before entering the intersection. Thus, if a motorist is in or very near the intersection when the yellow signal appears, he or she can probably traverse the intersection at normal traffic speed. On the other hand, a stop is indicated if the motorist is some distance from the intersection at the beginning of the yellow light interval.
Although the traffic control system described above is in common use throughout the United States and in many other parts of the world, it has a serious disadvantage which has contributed to many intersection collisions. A "dilemma zone" exists at a distance from the intersection whereat, upon actuation of the yellow signal, the motorist could conceivably either stop before the intersection or proceed through it before the red light interval. Upon encountering a yellow signal in the dilemma zone, a motorist must quickly (i.e., in a few seconds or less) decide whether to proceed or stop. The ability of a vehicle to stop or clear an intersection upon encountering a yellow light in the dilemma zone depends upon a number of factors including: (1) the driver's reaction time; (2) the breaking performance of the vehicle; (3) the speed of the vehicle; (4) the acceleration performance of the vehicle; (5) the road surface coefficient of friction; (6) the grade (i.e., incline, flat or decline); and (7) the distance from the intersection. All of these factors must be quickly taken into account and the proper decision reached to avoid making one of the following two mistakes: (1) trying unsuccessfully to stop before reaching the intersection; and (2) trying unsuccessfully to clear the intersection before the red interval. Numerous vehicular accidents have been attributed to both types of mistakes.
To reduce the hazards associated with the dilemma zone, it has heretofore been proposed to lengthen the yellow light interval and also to provide an interval between the commencement of the red light interval for traffic in one direction and the green light interval for cross traffic. Although both of these proposals may have some positive safety effect, they tend to contribute to inefficiencies in traffic flow because more vehicles are kept waiting longer at intersections. Furthermore, aggressive drivers may anticipate longer yellow light intervals and drive accordingly, often by accelerating when the yellow interval commences. A particularly dangerous situation occurs at an intersection where one driver is accelerating to clear the intersection during a yellow light interval and a cross traffic driver attempts to enter the intersection immediately upon or even prior to the commencement of his or her green light interval.
The present invention addresses the safety and efficiency problems of prior art traffic control systems.